The present invention relates to a unit to form pellet elements.
It is known that in many industrial processes for example in the chemical and foodstuff fields, the production cycle includes the formation of pellet elements starting from materials which are kept to the fluid state, that is the formation of substantially ball-shaped portions which are transferred and solidified on suitably-cooled conveyor belts.
In some cases the material thus fractionated may be an intermediate product adapted to further workings, but in other cases it already constitutes a final product. The pellet elements are made using various apparatus which substantially can be divided into two different types.
One type of known apparatus involves a series of dispensing nozzles located above the conveyor belt and transversely thereto, which continuously dispense predetermined amounts of material in the form of drops falling onto the conveyor belt surface. This type of apparatus however has serious drawbacks in that the static delivery of the fluid material onto a moving conveyor belt brings about an important deformation of the falling drops. Actually the drops will tend to take an elongate form losing their substantially ball-shaped conformation. In addition, depending upon the viscosity of the material and the conveyor belt feed speed, the separation between subsequent pellets delivered from the same nozzle may not occur.
In order to overcome the drawbacks encountered with this type of apparatus attemps have been made to use a second type of apparatus in which the drops of material are practically distributed onto the conveyor belt by means of movable dispensing holes moving at the same speed as the feed speed of the conveyor belt. This second type of apparatus generally comprises one fixed feeding cylinder the axis of which is transverse to the feed direction of the conveyor belt and which exhibits a number of feed holes along the generatrix of the feeding cylinder itself, at the lowest position thereof. Provided externally and in contact with the feeding cylinder is a second coaxial dispensing cylinder, the peripheral rotational speed of which is substantially coincident with the feed speed of the conveyor belt. Such second dispensing cylinder has a number of suitably spaced apart delivery holes which come in register with the feed holes of the first cylinder and therefore enable the issue of drops of material to the fluid state which do not lose their ball-shaped configuration even when they come in contact with the conveyor belt due to the absence of relative speed between said belt and the delivery holes.
But also this second type of known apparatus has limits and serious drawbacks, although it produces pellet elements of a satisfactory quality.
Actually these known apparatus are of complex and delicate construction and therefore expensive, due to the high precision required in coupling the inner static cylinder to the outer movable one. In addition, if in operation a partial ovalization of one cylinder occurs, the apparatus becomes useless and therefore must be replaced. They also have poor operative flexibility since they are provided with delivery holes spaced apart according to a fixed pitch. Therefore, the amount of fluid material used being equal, it is possible to accomplish pellet elements having only one and the same size.
It is not even possible to adjust the apparatus operation to the varying viscosities of the materials to be made into pellets. If one wishes to make the production of pellet elements suit the different types of fluid materials or make it meet different size requirements, it is necessary to replace the dispensing cylinder, which involves high costs also due to the down time as a result of the needed replacement.